1. Field of the Invention
The present invention relates to a turn assisting mechanism for a vehicle such as a lawn mowing vehicle, an agricultural tractor, etc., and, more specifically, to a turn assisting mechanism capable of lifting up front wheels of a lawn mowing vehicle that travels on lawn in a golf course to mow the lawn from the ground so that a wheel nearest to an axis of turning may not slide on the lawn to damage the same when the lawn mowing vehicle makes a U-turn.
2. Description of the Related Art
Recently proposed autonomous lawn mowing vehicle is capable of carrying out an unmanned mowing operation on lawns in holes of a golf course. The unmanned mowing operation must be carried out in such a way that strips of a fixed width of zones mowed against the lie of lawns and those of zones mowed for the lie of lawns are alternately arranged at accurate intervals. Moreover, the lawn mowing vehicle must be not only capable of making a U-turn along a turning circle of the smallest possible radius but also capable of quickly moving to the next strip for mowing.
An automatic lawn mowing vehicle disclosed in JP-A No. 1-108909 is provided with a four-wheel steering mechanism that turns the front and the rear wheels of the automatic lawn mowing vehicle in opposite directions, respectively, to enable the automatic lawn mowing vehicle to turn along a turning circle of the least possible turning radius.
The smaller the radius of a turning circle along which the lawn mowing vehicle turns around, the closer is the wheels of the lawn mowing vehicle to the center of the turning circle. Therefore, the difference in surface speed increases between a portion of each wheel farther from the center of the turning circle and a portion of the same nearer to the center of the turning circle as the radius of the turning circle decreases. Consequently, the degree of slip of the tread relative to the lawns increases and damage is caused to the lawn when the lawn mowing vehicle makes a U-turn on the lawn along a turning circle of a reduced radius.
Portions of the lawn damaged by the wheels when the lawn mowing vehicle makes a U-turn come to have a brown color in a few days, spoiling the appearance of the lawns. Particularly, in a hole where the lawn mowing vehicle repeats a U-turn to traverse for mowing, the portion of the lawn where the lawn mowing vehicle made a U-turn become brown and give the lawn a poor appearance.